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powerpc/64: Don't trace code that runs with the soft irq mask unreconciled

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"Reconciling" in terms of interrupt handling, is to bring the soft irq
mask state in to synch with the hardware, after an interrupt causes
MSR[EE] to be cleared (while the soft mask may be enabled, and hard
irqs not marked disabled).

General kernel code should not be called while unreconciled, because
local_irq_disable, etc. manipulations can cause surprising irq traces,
and it's fragile because the soft irq code does not really expect to
be called in this situation.

When exiting from an interrupt, MSR[EE] is cleared to prevent races,
but soft irq state is enabled for the returned-to context, so this is
now an unreconciled state. restore_math is called in this state, and
that can be ftraced, and the ftrace subsystem disables local irqs.

Mark restore_math and its callees as notrace. Restore a sanity check
in the soft irq code that had to be disabled for this case, by commit
4da1f79227 ("powerpc/64: Disable irq restore warning for now").

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
This commit is contained in:
Nicholas Piggin 2019-05-02 15:21:07 +10:00 committed by Michael Ellerman
parent 502523fd1d
commit e2b36d5917
4 changed files with 20 additions and 13 deletions
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1
arch/powerpc/kernel/fpu.S
View File

@ -63,6 +63,7 @@ _GLOBAL(load_fp_state)
REST_32FPVSRS(0, R4, R3)
blr
EXPORT_SYMBOL(load_fp_state)
_ASM_NOKPROBE_SYMBOL(load_fp_state); /* used by restore_math */
/*
* Store FP state into memory, including FPSCR

13
arch/powerpc/kernel/irq.c
View File

@ -258,16 +258,9 @@ notrace void arch_local_irq_restore(unsigned long mask)
*/
irq_happened = get_irq_happened();
if (!irq_happened) {
/*
* FIXME. Here we'd like to be able to do:
*
* #ifdef CONFIG_PPC_IRQ_SOFT_MASK_DEBUG
* WARN_ON(!(mfmsr() & MSR_EE));
* #endif
*
* But currently it hits in a few paths, we should fix those and
* enable the warning.
*/
#ifdef CONFIG_PPC_IRQ_SOFT_MASK_DEBUG
WARN_ON(!(mfmsr() & MSR_EE));
#endif
return;
}

18
arch/powerpc/kernel/process.c
View File

@ -134,7 +134,8 @@ static int __init enable_strict_msr_control(char *str)
}
early_param("ppc_strict_facility_enable", enable_strict_msr_control);
unsigned long msr_check_and_set(unsigned long bits)
/* notrace because it's called by restore_math */
unsigned long notrace msr_check_and_set(unsigned long bits)
{
unsigned long oldmsr = mfmsr();
unsigned long newmsr;
@ -153,7 +154,8 @@ unsigned long msr_check_and_set(unsigned long bits)
}
EXPORT_SYMBOL_GPL(msr_check_and_set);
void __msr_check_and_clear(unsigned long bits)
/* notrace because it's called by restore_math */
void notrace __msr_check_and_clear(unsigned long bits)
{
unsigned long oldmsr = mfmsr();
unsigned long newmsr;
@ -526,7 +528,17 @@ void giveup_all(struct task_struct *tsk)
}
EXPORT_SYMBOL(giveup_all);
void restore_math(struct pt_regs *regs)
/*
* The exception exit path calls restore_math() with interrupts hard disabled
* but the soft irq state not "reconciled". ftrace code that calls
* local_irq_save/restore causes warnings.
*
* Rather than complicate the exit path, just don't trace restore_math. This
* could be done by having ftrace entry code check for this un-reconciled
* condition where MSR[EE]=0 and PACA_IRQ_HARD_DIS is not set, and
* temporarily fix it up for the duration of the ftrace call.
*/
void notrace restore_math(struct pt_regs *regs)
{
unsigned long msr;

1
arch/powerpc/kernel/vector.S
View File

@ -21,6 +21,7 @@ _GLOBAL(load_vr_state)
REST_32VRS(0,r4,r3)
blr
EXPORT_SYMBOL(load_vr_state)
_ASM_NOKPROBE_SYMBOL(load_vr_state); /* used by restore_math */
/*
* Store VMX state into memory, including VSCR.